This invention relates to crystal modifications or a crystalline toluene adduct (crystal having toluene of crystallization) of a fluoran compound that are useful as electron donating color formers in recording materials such as a pressure-sensitive recording material and a thermal recording material. The invention also relates to recording materials containing said crystal modifications and/or a crystalline toluene adduct, as well as a process for producing a specified crystal modification or a crystalline toluene adduct from said crystal modifications and/or crystalline toluene adduct.
Recording materials that make use of the color forming reaction between colorless or pale-colored electron donating color formers (hereunder referred to simply as "color formers") and organic or Inorganic electron accepting color developers (hereunder referred to simply as "color developers") are well known and classified as pressure-sensitive recording materials, thermal recording materials, electrothermal recording materials, etc. Pressure-sensitive recording materials which are typically described In Japanese Patent Publication No. 20144/1967, etc. are used in such fields as vouchers and printers on computers. Thermal recording materials which are typically described in Japanese Patent Publication No. 14039/1970, etc. have a broad range of applications including recorders for instrumentation, facsimile, printers and automatic ticket vending machines.
Such recording materials are required to exhibit high performance in various respects including whiteness of background, storage stability of the background, color rendition, sensitivity for color formation, initial color density and storage stability of a color image, and it is essential to use color formers that specifically suit these purposes. Color formers for use with pressure-sensitive recording materials must satisfy an additional important characteristic requirement for high solubility in inner-phase solvent(s) (capsule oil(s)). Fluoran compounds are extensively used as color formers with various types of conventional recording materials.
While many compounds have already been known as fluoran compounds, those which have structural formulas similar to the structural chemical formula [formula (1)] corresponding to the crystal modification of fluoran according to the present invention include the following three known types: fluorans of formulas (2), (3) and (4) as described in Japanese Patent Publication Nos. 32767/1974 and 17490/1974; fluoran of formula (5) as described in Japanese Patent Public Disclosure (Laid-Open) No. 123556/1985; and fluoran of formula (6) as described in Japanese Patent Public Disclosure (Laid-Open) No. 283183/1989. For the respective formulas (1)-(6), see below: ##STR1##
The fluoran of formula (2), however, has the problem that it has too low a solubility in inner-phase solvent(s) to be effectively used as a color former in pressure-sensitive recording materials. Pressure-sensitive recording materials using this fluoran exhibit low whiteness and lightfastness of the CB surface and the color image formed on those materials is also low in lightfastness. Thermal recording materials using the fluoran (2) are low not only in the lightfastness of the background but also in the dynamic sensitivity for color formation and the storage stability of the color image formed on those materials. As a further problem, if the fluoran under consideration is used in common pressure-sensitive recording materials which use a zinc salt of a salicylic acid derivative as a color developer (which recording materials are hereunder referred to as "conventional pressure-sensitive recording materials") and in common thermal recording materials which use bisphenol A as a color developer (which recording materials are hereunder referred to as "conventional thermal recording materials"), the color rendered is purplish black and additional toning is necessary to attain a pure black color.
The fluoran of formula (3) has the problem that its solubility in inner-phase solvent(s) is insufficient to justify its use as a color former in pressure-sensitive recording materials. Pressure-sensitive recording materials using this fluoran are low in the whiteness of the CB surface and its lightfastness is also insufficient. Thermal recording materials using the fluoran (3) exhibit not only low background whiteness but also insufficient storage stability of the color image formed on those materials.
The fluoran of formula (4) has the problem that it has too low a solubility in inner-phase solvent(s) to be effectively used as a color former in pressure-sensitive recording materials. Pressure-sensitive recording materials using this fluoran exhibit not only low whiteness of the CB surface but also insufficient lightfastness; in addition, the color image formed on those materials is low in lightfastness. Thermal recording materials using the fluoran (4) exhibit not only low whiteness and lightfastness of the background but also poor dynamic sensitivity for color formation; in addition, the storage stability of the color image formed on those materials is by no means sufficient. As a further problem, if the fluoran under consideration is used in conventional pressure-sensitive and thermal recording materials, the color rendered is greenish black and additional toning is necessary to attain a pure black color.
The fluoran of formula (5) is also insufficient in solubility in inner-phase solvent(s). A pressure-sensitive recording material using this fluoran exhibits low whiteness and lightfastness of the CB surface; in addition, the color image formed on those materials also exhibits low lightfastness. Thermal recording materials using the fluoran (5) exhibit not only low whiteness and lightfastness of the background but also poor dynamic sensitivity for color formation and insufficient storage stability of the color image formed on those materials. As a further problem, if the fluoran under consideration is used in conventional pressure-sensitive and thermal recording materials, the color rendered is reddish black and additional toning is necessary to attain a pure black color.
The fluoran of formula (6) also exhibits insufficient solubility in inner-phase solvent(s). Pressure-sensitive recording materials using this fluoran also exhibit insufficient lightfastness of the CB surface; in addition, the color image formed on those materials has only low lightfastness. Thermal recording materials using the fluoran (6) exhibit not only low whiteness and storage stability of the background but also poor dynamic sensitivity for color formation; in addition, the storage stability of the color image formed on those recording materials is insufficient. Further, if the fluoran under consideration is used in conventional pressure-sensitive and thermal recording materials, the color rendered is greenish black and additional toning is necessary to attain a pure black color.